Battery packs having smart circuitry, including battery fuel gauges and safety circuits, are used increasingly in portable electronics devices, for example, in cellular telephones, laptop computers, and in other portable electronics devices. The smart circuitry associated with these battery packs may however drain charge excessively from the batteries resulting in permanently reduced charge storing capacity. Uncharged batteries are particularly susceptible to damage from excessive discharge, for example discharge occurring during the time interval between manufacture and delivery to consumers. It is not uncommon for some products to remain in inventory for many months, up to one year or more, during which excessive discharge from smart circuits may occur.
In cellular telephone handsets, for example, the power-off current drawn by battery smart circuits may be substantial, at times exceeding 20 uA. This current will deeply discharge the battery over an extended time interval, possibly resulting in permanent damage to the battery.
Charging batteries before shipping reduces the tendency of battery circuits to become excessively discharged prior to delivery to end-users, but charging is burdensome on manufactures and suppliers.
The use of hibernation, or sleep, circuits in rechargeable battery packs to prevent excessive discharging is known generally. U.S. Pat. No. 6,072,250 entitled “Battery Pack Having Hibernate Circuit”, for example, discloses a rechargeable battery pack having a hibernate circuit that is disabled upon user actuation of a dedicated mechanical switch disposed on the battery pack. U.S. Pat. No. 6,144,186 entitled “Low Power enable Circuit”, discloses a rechargeable lithium ion battery pack that enters a sleep mode upon simulation of a low voltage, and exits sleep mode upon charging the battery.
The various aspects, features and advantages of the present invention will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description of the Invention with the accompanying drawings described below.